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Altamira Oriole

Art by Mimi Hoppe Wolf

Icterus gularis

The Altamira Oriole is widespread in subtropical lowlands of the Mexican Gulf Coast and northern Central America, and has extended its range into the United States within this century. In North America, Altamira Orioles occur only in semiarid South Texas. Most occur in the Lower Rio Grande Valley (LRGV), in native Tamaulipan thornscrub and riparian habitat, and occasionally in rural or suburban habitat (Oberholser 1974, Brush unpub. data). Throughout its range, the Altamira Oriole is a permanent resident. Although its distinctive and conspicuous hanging nest allows relatively easy confirmation as a breeding species, the inaccessiblity of the nest has made collection of information on breeding biology quite difficult. Altamiras now nest as far north as Kingsville (latilong 27097) and Zapata (latilong 26099) in small numbers, but have declined in some of their LRGV strongholds.

DISTRIBUTION: Altamira Orioles breed sparsely from the Kingsville and Zapata areas south through the ranch country to the LRGV (Cameron, Hidalgo, Willacy and Starr Counties in latilongs 26098, 26097, 25097). Very rare on BBS routes, Altamiras occur regularly, in numbers>10, on three LRGV Christmas Bird Counts (Santa Ana, Anzalduas-Bentsen, and Falcon Dam State Park; Root 1988), and irregularly or in very small numbers on four other LRGV counts and two other counts in the United States. The one TBBAP record further north at Artesia Wells (28099-C3) was a sighting of a single adult on 22 May 1992. No further evidence of breeding was observed but the atlaser noted that Altamiras had been recorded a number of times on the nearby Chaparral Wildlife Management Area (B. Ortego, pers. comm.). Their exact distribution and status are difficult to determine in much of the area, due to difficulty of access to large private ranches. Vagrant birds (Oberholser 1974) have occurred in El Paso (December 1956: immature, filmed) and San Antonio (Summer 1957).

SEASONAL OCCURRENCE: The breeding season for Altamira Orioles is fairly long, as evidenced by dates of nest construction (25 March through 8 July; Brush unpub. data). Adults have been observed carrying food to nests from 20 May through 31 July (Pleasants 1981, Brush & Bray unpub. data). Observations of banded adults at one nest and unbanded adults at another revealed double brooding (Brush & Bray unpub. data). Single Altamira Oriole eggs, presumably recently laid, were seen in low Altamira nests on 28 June and 7 July. More information is needed on breeding biology.

alornest.jpg (17866 bytes)

Photo by Robert Brashear

Unusual nesting site

BREEDING HABITAT: In the United States, Altamiras usually nest in Tamaulipan thornscrub or riparian forest, typically in protected nature preserves. A few pairs nest in rural or suburban yards, given the existence of at least 2-3 hectares (5-8 acres) of native habitat nearby. Most nests are built hanging over open space, at the edge of open fields, roads, or rivers (Pleasants 1981, Brush & Bray unpub. data), at heights of 3-11 m (10-36 ft.). Twelve tree species have been used in the Lower Rio Grande Valley, with many nests in recent years in Mexican ash (Fraxinus berlandierana), sugar hackberry (Celtis laevigata), and cedar elm (Ulmus crassifolia; Brush & Bray, unpub. data). Nests are sometimes found hanging from telephone wires and rarely, other artificial structures. Nests are made of the inner bark of trees, retama (Parkinsonia aculeata) leaves, various grasses, and occasionally Spanish moss (Tillandsia usneoides) and plastic twine.

Foraging habitat is denser than nesting habitat. Adults and fledglings often select areas with low, dense foliage, usually thornscrub or mixed habitat. Fledglings are often seen foraging in such habitats, even when not accompanied by adults.

STATUS: The first generally accepted Altamira Oriole specimen from the United States was collected in 1939, in Cameron County (25097) (Oberholser 1974). Altamiras probably increased slowly at first, with the first CBC record in 1947, and the first known nest in 1951. In the 1960s and 1970s, Altamiras became established at Santa Ana National Wildlife Refuge (26098-A2), where 24 nests were found in 1964 and at least 18 in 1974 (Pleasants 1993). A smaller population was established at the same time at Bentsen-Rio Grande Valley State Park (26098-B4). At Falcon Dam (26099-E2), the species was first noted in the early 1970s. Although still a common nester at Santa Ana in 1980 and 1981 (Carter 1986), by 1992 many former nesting areas were unoccupied (Brush & Bray unpub. data). CBC numbers declined after the early 1980s at Santa Ana and Brownsville (25097-H4,H5), while numbers on the Falcon Dam State Park CBC increased. During the 1993-1996 period, Altamira Oriole nesting populations have remained low at Santa Ana, while Falcon breeding populations and CBC numbers have reached their highest levels. The death of many large trees, apparently caused by the prolonged lack of flooding (due to construction of Falcon Dam in 1953), periodic droughts, and the two hard freezes of the 1980s, appears to be the main factor causing decline of Altamiras at Santa Ana and possibly elsewhere in the LRGV. Altamiras recently nesting at Santa Ana have used mainly field edge habitat (Brush & Bray, unpub. data).

Cowbirds may have had some impact on Altamiras, as well. Both Bronzed and Brown-headed Cowbird eggs have been found in Altamira nests (Friedmann & Kiff 1985, Brush & Bray, unpub. data), and in 1996 one Bronzed Cowbird juvenile was observed being fed by an Altamira Oriole pair (Brush & Bray unpub. data).

With further field work in the South Texas ranch country and the Lower Rio Grande Valley, some additional nesting areas may be found, and range expansion may continue slowly into northern sections of the Tamaulipan biotic province. Maturation of re-vegetated fields in the LRGV may provide additional habitat, if suitable nest trees are available. The status of Altamira Orioles in the United States remains precarious. Text by Tim Brush (ca 1994)

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